In messages that consumers receive from advertisements, whenever a consumer sees an advertisement, they receive a message. The consumer can respond to the message in a number of ways. Identifying with it and being alienated by it are two of these possible responses.
If a person identifies with a message, they like it and feel that it applies to their lives. For example, a parent who sees an ad for a car that emphasizes its safety features and shows a child being kept safe by those features may identify with the message. They may feel that the message speaks to things that are important in their lives. This is, of course, what advertisers want.
If a person is alienated by a message, it means they are repelled or pushed away by it. For example, an environmentalist might be alienated by an ad for an SUV that shows it splashing through streams and driving over untouched landscapes. This message would go against their core values and they would feel very unhappy when they viewed it.